1. Technical Field
Embodiments of the present invention relate to an optical scanner including a laser diode array, and an image forming apparatus incorporating the optical scanner.
2. Related Art
Due to a recent trend of high productivity and high density in image forming apparatuses, optical scanners provided thereto have achieved high productivity and high image quality by achieving an increase in the number of light sources and in the number of rotation of a rotating deflector such as a polygon scanner. If a rotating light deflector rotates at a higher speed for enhancing productivity of an image forming apparatus, the bearing of the rotating deflector generates heat. Therefore, there is a limit to an increase in rotation of a rotating light deflector. By contrast, it is known that an increase in the number of light sources achieves high productivity and high density in image forming apparatuses.
Some techniques have been disclosed to increase the number of light sources. For example, Japanese Patent No. JP-3681555-B (Japanese Patent Application Publication No. JP-2000-098278-A) discloses a technique in which multiple luminous fluxes intersect to be condensed on a rotating light deflector with a laser diode having a single light source. Japanese Patent No. JP-3451467-B (Japanese Patent Application Publication No. JP-H10-003047-A) discloses a technique in which light fluxes are synthesized so as to be arranged at given beam pitches after passing through a coupling lens. Further, Japanese Patent Application Publication No. JP-2009-294238-A discloses a technique of an optical scanner in which the number of parts is decreased by removing a holder to which a light source is attached, and the light source is easily replaceable and adjustable in its rotation direction after installation.
The techniques disclosed in JP-3681555-B (JP-2000-098278-A) and JP-3451467-B (JP-H10-003047-A) increase the size of each device when compared with a device in which a laser diode array having multiple light sources is provided in one package. Further, the laser diode array needs rotation adjustment and fixation to obtain a desired writing density. However, since the laser diode array is small, a separate holder is provided to hold the laser diode array. Therefore, the rotation of the laser diode array is adjusted with this holder. Accordingly, the number of parts increases, which makes it difficult to reduce the size of the optical scanner. Further, the technique disclosed in JP-2009-294238-A cannot enhance operability in adjustment of beam pitches for positioning and adjusting the rotation direction of the laser diode array.